The present invention relates to macrophage colony stimulating factors (M-CSF) and, more specifically, to macrophage colony stimulating factor-.gamma. (M-CSF.gamma.).
Colony stimulating factors are proteins that influence the growth and differentiation of cells responsible for the formation of blood in the body and have traditionally been defined by their ability to stimulate growth of colonies of bone marrow cells in semi-solid media. Macrophage colony stimulating factor ("M-CSF") is a subclass of colony stimulating factors and plays a role in the regulation of immune responses by potentiating the proliferation and differentiation of macrophages from immature hematopoietic progenitor cells, and inducing effector functions of mature macrophages including secretion of interferon-.gamma., tumor necrosis factor and non-M-CSF colony stimulating activities. Native mammalian M-CSF is a glycosylated, disulfide-linked homodimer with molecular weights ranging from 45 to 90 kilodaltons (kDa). Disulfide bond formation is required for biological activity.
Recently, two human M-CSF complementary DNAs (cDNA) encoding distinct M-CSF proteins have been isolated. Kawasaki et al. (Science 230:291, 1985) first reported the isolation of a cDNA clone from a human pancreatic carcinoma cell line, MIA-PaCa. This cDNA, when expressed in COS-7 cells, produced M-CSF activity as judged by its ability to cause proliferation and monocytic colony formation from murine bone marrow cells. The cDNA encoded a protein of 256 amino acids that included a 32 amino acid signal sequence and a putative transmembrane region of 23 hydrophobic amino acids near its carboxyl end. It was proposed that this protein was synthesized as a membrane-bound precursor that was then proteolytically cleaved, releasing mature M-CSF.
A second M-CSF cDNA was isolated by Wong et al. (Science 235:1504, 1987), who reported that this cDNA encoded a protein of 554 amino acids. The larger coding region was due to an in-frame insertion of 894 bp after amino acid 181. The coding regions from both cDNAs share the same amino- and carboxyl-terminal amino acids including the signal sequence and transmembrane regions. The larger cDNA, upon expression in COS-7 cells, was found to yield a biologically active protein as judged by its ability to form monocytic colonies from human and murine bone marrow cells. It was suggested that the two M-CSF cDNAs were formed by alternate splicing of mRNA. In order to distinguish the two distinct proteins identified and isolated by Kawasaki et al. and Wong et al., they are referred to herein as M-CSF.alpha. and M-CSF.beta., respectively.
The existence of several distinct but related species of M-CSF now raises the possibility that these and possibly other different forms may be responsible for mediating the different biological activities described above. In order to fully elucidate the biological role of M-CSF activity, it is thus necessary to identify and characterize the factors responsible for M-CSF activity.